This invention relates to a screw-based incandescent lamp type fluorescent lamp with a luminous tube, a ballast and a operating member enclosed in an outer tube.
Fluorescent lamps of this type are used for household illumination and other applications since they can be fitted in lamp sockets for conventional incandescent lamps and have a decided superiority in luminous efficiency over the incandescent lamps.
With one such fluorescent lamp, if a luminous tube and a ballast, having equivalent power consumption of 20 W are incorporated in a bulb or outer tube with a diameter of 120 mm or less, for example, the temperature inside the outer tube will be increased to reduce the total luminous flux of the lamp by approximately 20 to 30% as compared with the brightness obtained with use of a naked luminous tube. Further, the lamp voltage is reduced by approximately 20 to 30%, and the lamp current is increased by approximately 10 to 15%, resulting in the increase of a ballast loss, so that the lamp requires a large-sized ballast and consumption of emitter of a lamp electrode becomes extremely large thereby reducing the lamp life. Accordingly, the lamp requires a large-sized outer tube, a filament of a larger diameter and a great amount of emitter attached to the electrode.